The contents that adheres to is the substance of general urbanbreathnyc.comistry class 26. In this class we proceed the discussion of Quantum Numbers and their usage in Electron Configurations and also the relationship of electron configuration to the routine properties of the elements.

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Electron Configuration

Electron configurations space the summary of wherein the electrons are approximately a nucleus. Together we learned earlier, each neutral atom has a number of electrons same to its number of protons. What we will do now is place those electrons into an arrangement approximately the cell core that indicates their energy and the form of the orbital in i m sorry they room located. Here is a an introduction of the species of orbitals and also how many electrons each can contain:


So based on what us know about the quantum numbers and also using the graph above, you require 2 electron to fill an s orbital, 6 electrons to fill a ns orbital, 10 electrons to to fill a d orbital and 14 electrons to to fill the f orbital. But what we haven\"t debated is how these orbitals obtain filled...the bespeak of fill.

Order that Fill

The bespeak in which electrons are inserted into the orbitals is based on the order of their energy. This is described as the Aufbau principle. The lowest energy orbitals to fill first. As with the quantum numbers themselves this bespeak was established by calculation and also is summarized by the complying with chart:


or you can just usage the routine table:


How to write an Electron Configuration

The symbols provided for creating the electron configuration begin with the covering number (n) followed by the type of orbital and also finally the superscript indicates how many electrons space in the orbital.


For example:

Looking in ~ the routine table, you have the right to see that Oxygen has actually 8 electrons. Based upon the order of to fill above, this 8 electrons would fill in the following order 1s, 2s and also then 2p. So Oxygen\"s electron configuration would certainly be O 1s22s22p4.

Special Cases

Configurations of ions current a special situation of electron configuration and additionally demonstrate the factor for the development of those ions in the very first place.

If you have to write the complete electron construction for an anion, climate you are just including additional electrons and the configuration is just continued.

For example, we recognize that Oxygen constantly forms 2- ions once it provides an ion. This would add 2 electron to its normal configuration make the new configuration: O2- 1s22s22p6. With 10 electrons you need to note the oxygen\"s electron configuration is now specifically the same as Neon\"s. Us talked around the truth that ions form because they deserve to become much more stable v the get or lose of electrons to become like the noble gases and now you have the right to actually see exactly how they come to be the same.

The electron configurations because that Cations are additionally made based on the number of electrons yet there is a slight difference in the method they are configured. Very first you have to write their regular electron configuration and also then when you eliminate electrons you have to take them from the outermost shell. Note that this is not always the same method they to be added.

Here is an example of what i mean:

Iron has actually 26 electron so its typical electron configuration would certainly be: Fe 1s22s22p63s23p64s23d6

When we make a 3+ ion because that Iron, we need to take the electrons from the outermost shell an initial so that would be the 4s covering NOT the 3d shell: Fe3+ 1s22s22p63s23p63d5

One other note on writing electron configurations: A brief cut. As soon as writing some of the reduced table configuration the full configuration have the right to be reasonably long. In these cases, you have the right to use the vault noble gas to abbreviate the configuration as shown below. Friend just have actually to end up the construction from where the noble gas leaves it:



As v every various other topic we have covered to date there are exceptions to the order of fill as well. But based upon the electron construction that room generated, this exceptions are easy to understand.

In the d block, especially the groups containing Chromium and Copper, there is an exemption in exactly how they room filled.

Here space the really configurations:


In these columns, the 4s and 3d

Practice, Practice, Practice

There are lots of quizzes on electron configurations you can practice with located here

Orbital Diagrams

Another means to represent the stimulate of fill for one atom is by making use of an orbital diagram regularly referred to together \"the small boxes\":


The crate are supplied to represent the orbitals and also to show the electrons put in them. The bespeak of fill is the same but as you deserve to see from above the electrons are inserted singly into the boxes before filling them with both electrons. This is referred to as Hund\"s Rule: \"Half fill prior to you full fill\" and again this dominion was established based on energy calculations that suggested that this to be the method atoms actually dispersed their electrons right into the orbitals.

Periodic Properties

One that the yes, really cool things about electron construction is their partnership to the periodic table. Basically the regular table was created so that elements with comparable electron configurations would be aligned into the same groups (columns).


Periodic Table mirroring last orbital filled because that each element

The routine table shown over demonstrates exactly how the construction of each aspect was set so that the critical orbital to fill is the same other than for the shell. The factor this was done is the the construction of an aspect gives the aspect its nature and similar configurations yield similar properties.

Let\"s walk through few of the routine Properties that room influenced straight by the electron configuration:

Atomic Size

The dimension of atoms rises going down in the periodic table. This need to be intuitive because with each heat of the table you are including a shell (n).

What is not as intuitive is why the dimension decreases indigenous left to right. However again the building of the electron configuration offers us the answer. What room you doing together you go across the regular table? Answer, adding protons come the cell core and including electrons to the valence covering of the element. What is not transforming as you overcome a period? Answer, the inner covering electrons.

So think of that this way, the inner covering electrons room a shield versus the traction of the nucleus. Together you overcome a period and rise the number of protons in the cell core you rise its pull but because you room only adding electrons come the brand-new shell the shield is not increasing however remains the same all the method across. This method the pull on the electron being added to the valence covering is raising steadily all the means across. What wake up if you traction harder on the electrons? Well, castle come closer to the nucleus and also the size of the atom decreases. The result of the cell nucleus pulling top top the electrons being added throughout a period is called the reliable nuclear charge and also is calculated together ZEff = #protons - main point # Electrons.

So for example the pull felt through Sulfur would be ZEff = 16 - 10 = +6



Electronegativity might be the most necessary of the periodic properties you have the right to learn and also understand due to the fact that so numerous other nature are rely on its value. Electronegativity is one atoms capability to traction electrons in the direction of itself.

Electronegativity is typically expressed by the Pauling Scale and also the worths were established experimentally. The table below shows the range values because that the elements.


The electronegativity values increase from left to right and bottom to optimal in the periodic table excluding the Noble gases. The most electronegative facet is Fluorine.

From this electronegativity worths we deserve to derive the fads of two various other periodic properties: Ionization Energy and Electron Affinity.


Ionization Energy

Ionization power is the amount of energy required to remove an electron indigenous an atom. Every ionization energies are positive values because every one of these removals (even those for aspects that type positive ions) require input of energy. The an ext electronegative the element, the greater the ionization eneregy.

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Electron Affinity

The Electron Affinity that an aspect is the quantity of energy gained or released with the addition of an electron. The electronegativity and Electron Affinity increases in the same pattern in the routine table. Left come right and also bottom to top.